In the softening of a hard water, bicarbonate hardness can be reduced by the application of heat to that water in accordance with the well known reaction: ##EQU1## The greater portion of the CaCO.sub.3 which is formed by this reaction is precipitated and removed as a sludge. The CO.sub.2 is vented to the atmosphere. As a result the pH of the hard water is increased. When it is required to remove magnesium ions from water, which ions concurrently carry with them some of the silica impurities of the water, a further increase in pH of the water is produced by the addition of lime to provide an additional softening of the water and to eliminate the silica impurities. In either case, the precipitation of the hardness is incomplete because of the slow kinetics of the chemical reactions involved, and the hardness compounds continue to precipitate after the water has been discharged from the softening equipment.
The customary method for preventing the formation of scale deposits such as the above in water which has been softened is the acidification of that water by means of a mineral acid or by the injection of CO.sub.2 from an external source, either of which increases the production costs of conventional water softening techniques. To reduce such costs, a need has arisen for improvements which do not rely upon acidification or the use of CO.sub.2 from an external source to prevent scaling by the softened water.
Prior publications relating to the softening of hard water include U.S. Pat. No. 4,018,656 and the references cited therein, and a publication entitled "Conversion of Desalination Plant Brines to Solids," by W. L. Standiford, Research and Development Progress Report No. 636, Contract 14-30-2660, U.S. Department of the Interior, 1970. However, these prior publications do not teach or suggest the concept of using self-generated CO.sub.2 for stabilization of softened water.